Process for producing a preweakened automotive interior trim piece for covering an air bag installation in an automotive vehicle

ABSTRACT

A process for preweakening the inside of an automotive trim piece cover layer of various constructions by use of a laser beam so as to enable formation of an air bag deployment opening in the trim piece formed at the time the air bag deploys. The laser beam impinges the inside surface of the cover to form a groove scoring or spaced perforations to form a preweakening pattern. A robot arm may be used to move a laser generator so as to form the preweakening pattern. The laser beam can be controlled in accordance with sensed conditions to achieve accurate preweakening, and may also be used to trim substrate panels and to perform other cutting operations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. Ser. No. 09/816,955, filed Mar.23, 2001 now U.S. Pat. No. 6,808,197, which is a division of U.S. Ser.No. 09/339,885, filed Jun. 25, 1999, which is now U.S. Pat. No.6,267,918, issued Jul. 31, 2001, which is a division of U.S. Ser. No.09/063,141, filed Apr. 20, 1998, which is now U.S. Pat. No. 6,294,124,issued Sep. 25, 2001, which is a division of U.S. Ser. No. 08/332,565,filed Oct. 31, 1994 which is now U.S. Pat. No. 5,744,776, issued Apr.28, 1998.

FIELD OF THE INVENTION

The present invention concerns cutting and scoring of covers forautomotive trim pieces enclosing air bag safety devices.

BACKGROUND OF THE INVENTION

Air bag safety systems have come into widespread use in automotivevehicles and light trucks and have been proposed for use in passengertrains and airplanes.

Such systems comprise an inflatable cushion, commonly referred to as an“air bag” which is stored folded in a storage receptacle and then veryrapidly inflated, as with gas from a pyrotechnic gas generator, when acollision of the vehicle is detected by sensors. The air bag is therebydeployed in a position to absorb the impact of the driver or apassenger.

It is necessary that the folded air bag be stored in an enclosed secureenvironment within the passenger compartment, protected from tampering,and yet be allowed to properly deploy into the passenger compartment asthe air bag is inflated.

It is critical that the air bag deploy within milliseconds of activationof the system in order to protect the occupant.

As noted, the air bag is enclosed within a storage receptacle, which istypically mounted behind an interior trim piece, such as a steeringwheel cover in the case of the driver's side air bag, or a section ofthe instrument panel, in the case of the passenger's side air bag. Ithas been proposed to also provide side impact air bags in the vehicledoors.

One or more air bag deployment doors normally overlie the air bagreceptacle and are forced open when the air bag is inflated to allowdeployment of the air bag through the opening created by the door panelmovement.

As described in U.S. Pat. No. 5,082,310 issued on Jan. 21, 1992 for an“Arrangement for Providing an Air Bag Deployment Opening”, a seamlessconstruction is advantageous in which the deployment door panels are notseparately delineated within the expanse of the trim piece, but rather asmooth uninterrupted surface is provided extending over the deploymentdoor substrate panels.

This construction necessitates severing portions of the covering of thetrim piece in order to allow the door panels to hinge open.

Severing has been achieved by the pressure of the inflating air bag, orby various other methods which have been proposed, such as linear energydevices described in copending U.S. Ser. No. 08/279,225, filed Jul. 22,1994. See also U.S. Ser. No. 08/027,114, filed Mar. 4, 1993, and U.S.Pat. Nos. 5,127,244 and 4,991,878 describing pyrotechnic elements usedto cut the outer cover layer of the trim piece.

Cutter blades have also been proposed which are forced outwardly by theair bag inflation to assist in cutting the cover layer, but theseoutwardly swinging elements can present a potential hazard to a vehicleoccupant seated in front of the deployment door.

Automotive interior trim covering materials such as vinyl plastic arerelatively tough and difficult to sever, and also a predeterminedsevering pattern is necessary for proper door panel opening, such thatheretofore preweakening grooves have been formed in the trim cover in apredetermined pattern to insure proper opening.

It has heretofore been proposed to provide an “invisible seam”installation in which the deployment door pattern is totally invisibleto a person seated in the vehicle passenger compartment, and even faintoutlines or “witness” lines are desirably avoided.

Scoring of the covering layer from the inside, if not done accurately,can over time become at least faintly visible from the exterior of thetrim piece.

Fabrication of the automotive interior trim pieces with preweakeninggrooving particularly for invisible seam applications is thus adifficult manufacturing challenge.

First, the groove depth must be carefully controlled in order to achievereliable rupture of the outer cover at exactly the right time during theair bag deployment event.

If the groove is too shallow, the thickness of the remaining materialmay be too great, presenting excessive resistance to severing, delayingair bag deployment. Conversely, if too little material remains, overtime cracking may be result, or at least allow the appearance ofexternally visible “witness” lines.

The preweakening effect may also be less effective if the grooves aremolded-in during the process since it has been found that cutting intoplastic material such as vinyl has a better preweakening effect comparedto molding-in the groove during the initial manufacture of the item.

The high pressures used in injection molding can cause a “crazing”effect at the thinned bridging material extending over the gap definedby the groove. This crazed zone is rendered more visible as the part isremoved from the mold, particularly if the part is not completely cooledwhen it is being removed.

The net effect is that the molded groove becomes visible on the exteriorside.

It is difficult to accurately and reliably control the depth ofmechanical cutting of component materials such as sheet vinyl, since thematerial is variably compressed by the pressure of a cutting instrument.

U.S. Pat. No. 5,082,310, referenced above, describes a partial cuttingprocedure which is intended to enable accurate control over the depth ofthe cut into a sheet of pliant plastic material such as a vinyl skin.However, a purely mechanical cutting operation still has other inherentaccuracy limitations and is slow to execute.

Also, some cover materials have irregular inside surfaces, i.e., drypowder slush processes create such irregularities. If the groove depthwere constant, this results in an irregular thickness of the remainingmaterial. This leads to erratic performance as the resistance to openingpressure will vary greatly.

The groove width is also important, in that if a too narrow groove iscut into many plastics, a “self healing” may occur, particularly atelevated temperatures in which the groove sides will re-adhere to eachother, causing the preweakening effect to be erratic or neutralized.

The required groove width also varies with the notch sensitivity of thematerial being preweakened.

A further difficulty is encountered in assembling the preweakenedcomponent to the interior trim structure so that the lines ofpreweakening are properly registered with the other components. Forexample, the vinyl skin in a skin and foam instrument panel must beaccurately positioned on the instrument panel substrate and thedeployment door substrate panels so that the preweakening lines arestressed as the door edges hinge out under pressure from the air bag.

This alignment requirement creates manufacturing difficulties andincreased costs particularly since a variety of forms of instrumentpanel structures are employed, i.e., skin and foam, vinyl clad, hardplastic with a finished surface, etc., since a variety of formingtechniques are employed, i.e., vacuum formed calendared plastic sheet,dry powder slush molded, injection molded, etc. A leather covering latersometimes may be used in lieu of a vinyl plastic covering layer.

Accordingly, it is an object of the present invention to provide aprocess for preweakening trim components overlying an air baginstallation by groove scoring which is highly accurate in productionimplementation, and which may be efficiently integrated into the trimpiece manufacture to lower costs and improve results.

SUMMARY OF THE INVENTION

According to the invention, the preweakening groove scoring of asmoothly contoured trim piece cover material overlying an air bagreceptacle is carried out by the use of a laser beam which is controlledand guided so as to produce grooves of a precise depth and width formedby the laser beam energy into the undersurface of various trim piececover materials such as a vacuum formed sheet of vinyl.

A sensor provides a feedback signal allowing relative positioning of theworkpiece and/or varying of the laser beam source intensity or toprecisely control the groove depth to achieve a constant thickness ofthe remaining material.

The workpiece and laser beam source can be mounted for relative movementin a two-axis positioner table, or alternatively, a system of movablereflectors can optically generate the groove pattern.

A five axis robotic arm can also be used to guide the laser beam sourcein the required pattern extending in three dimensions, and in process orpost-process gauging can also be utilized to correct the laser and robotcontrol and improve results.

The laser beam preweakening groove scoring can be carried out on thecover piece prior to its incorporation into the trim piece or suchgroove scoring can be carried out after attachment to a substrate orother trim elements grooving the underlying substrate and partiallyscoring the cover layer at the same time to create a deployment doorsubstrate panel while preweakening the cover material.

The laser beam apparatus can further be utilized to trim the assembledtrim piece.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective diagrammatic view of a laser beam scoringapparatus having a trim piece disposed therein being preweakened in apredetermined pattern by laser beam groove scoring.

FIG. 2 is a fragmentary view of a trim piece having a preweakeninggroove formed therein back filled with a filler material.

FIG. 3 is a perspective diagrammatic view of another form of the laserbeam scoring apparatus according to the invention and having a trimpiece disposed therein being preweakened in a predetermined pattern bylaser beam groove scoring.

FIG. 4 is a perspective, simplified representation of a preferred robotarm form of the laser beam scoring and cutting apparatus together havinga trim piece disposed therein being trimmed and preweakened in apredetermined pattern by laser beam groove scoring.

FIG. 4A is a perspective, simplified view of the robot arm laser beamscoring and cutting apparatus of FIG. 4 with an added robot arm forin-process gauging of the trim piece surface.

FIG. 5 is an enlarged, fragmentary sectional view taken through a drypowder slush molded cover and along a preweakened laser scored groove.

FIG. 5A is a sectional view of the cover of FIG. 5 taken across thepreweakening groove.

FIG. 6 is an enlarged, fragmentary sectional view taken through smoothcalendared sheet stock, vacuum formed into an air bag installation coverlayer, laser scored from the undersurface.

FIG. 7 is a front perspective view of a steering wheel cover whichoverlies an air bag installation and which has been preweakened in apredetermined pattern with a laser scored grooving.

FIG. 8 is an enlarged sectional view of a portion of the steering wheelcover shown in FIG. 7, the section taken across the laser formed groove.

FIG. 9 is an enlarged sectional view of a vinyl cladding cover materialwhich has been laser scored with grooves of various depths.

FIG. 10 is an enlarged sectional view of a layer of vinyl claddingvacuum formed to a thermoplastic substrate such as for an instrumentpanel trim piece which has been laser scored with grooves of variousdepth.

FIG. 11 is an enlarged sectional view of a leather covering materialwhich has been pretreated and subsequently laser scored through thepretreated region.

FIG. 12 is an enlarged sectional view of the leather covering materialwhich has been laser scored without the pretreatment in the region ofthe scoring.

FIG. 13 is an enlarged sectional view of a cosmetic covering such as afabric material having a backing layer, preweakened by being laserscored to penetrate the backing layer.

FIG. 14 is an enlarged sectional view of a composite cover comprised ofa metal substrate panel with an overlying skin, both preweakened by alaser-formed groove.

FIG. 15 is an enlarged sectional view of molded urethane with amolded-in-place scrim, both preweakened with a laser formed groove.

FIG. 16 is a fragmentary section of a trim piece workpiece in which thesubstrate is being cut at the same time the covering layer is beingscored.

FIG. 17 is a sectional view of a trim piece being preweakened by beingperforated with an intermittently generated laser beam.

FIG. 18 is a sectional view of a trim piece being scored to variabledepths with a pulsating laser beam.

FIG. 19 is a fragmentary plan view of a laser scored groove withtraverse slits added to establish local weakening to control the site atwhich tearing is initiated.

DETAILED DESCRIPTION

In the following detailed description, certain specific terminology willbe employed for the sake of clarity and a particular embodimentdescribed in accordance with the requirements of 35 USC 112, but it isto be understood that the same is not intended to be limiting and shouldnot be so construed inasmuch as the invention is capable of taking manyforms and variations within the scope of the appended claims.

The present invention is concerned with preweakening of an automotiveinterior trim piece such as a steering wheel cover or an instrumentpanel overlying an air bag receptacle stored behind the trim piece. Thesurface of the interior trim presented to the passenger compartment mustbe aesthetically pleasing rather than starkly utilitarian. There hasalso been developed a preference for eliminating any suggestion of thepresence of the stored air bag. In the past, separately defineddeployment doors have been fit into an opening in the instrument panel.In the case of a wheel cover, visible delineations segmenting the coverto form deployment doors have been provided.

Internal grooves have also been provided, typically molded into the trimpiece itself.

As described above, molded grooves have sometimes resulted in exteriorlyvisible “witness” lines, since the high injection pressures forcing theplastic through the narrow gap remaining above the groove has resultedin a crazing pattern, as well as slight cracking when the part isremoved from the mold.

The present invention comprises the process of laser scoring to obtainthe preweakening internal groove after the cover has been molded orotherwise formed.

A laser beam is directed at the cover layer or other trim piececomponent to score the component along a path defining the desiredpattern matching the deployment doors.

The laser scoring has been found to result in elimination of anyexteriorly visible lines, even where minimum material remains above thescoring groove.

Referring to a first embodiment (FIG. 1) of a laser scoring apparatus 10suitable for practice of the invention, a small (25-150 watt) carbondioxide gas laser source 12 producing a coherent infrared laser outputbeam 14 at 10.6 micron wavelength is driven to effect controlled scoringof a region of a polymer sheet material instrument panel cover 16extending over an air bag installation when installed. The cover 16 ismoved relative the laser source 12 to cause tracing of a particularpattern at a precise rate of scoring by a multiaxis positioning system17. The laser output beam 14 is focused to a spot or small diameterpencil beam using one or more focusing elements 18 to cause formation ofa score line 20 of acceptable width. The presence of the score line 20which is cut to a significant depth generates a seam which is invisiblewhen viewed from outside face 21 of cover 16 (FIG. 2). The outside face21 of cover 16 forms the cosmetic surface presented to occupants of thevehicle.

The width of the score line 20 is generally minimized in typicalapplications but self healing may be avoided when necessary by makingwider cuts which may be backfilled with a material having physicalproperties having generally beneficial physical properties for improvingbursting of the invisible seam during air bag operation in the vehicle.

For example and referring to FIG. 2, a portion of a polymer sheetinstrument panel cover 16 with a wide score line 22 and with filler 24comprising a cured in place silicone rubber bead is shown. Filler 24provides mechanical support in a similar fashion as was experiencedbefore polymer was removed by the laser. The mechanical support providedby filler 24 prevents deterioration of cover 16 over the lifetime of thevehicle.

Typical focusing elements for infrared laser 12 comprise galliumarsenide or germanium refractive lens members, or gold reflectivemembers. Several alternate laser types will achieve good results andlaser source 12 may be an excimer, solid state, argon gas, or diodelaser. However, the carbon dioxide laser is likely to be the leastexpensive in both initial cost and over the required lifetime.

If laser source 12 produces continuous output, the depth of the scoreline 20 is controlled by the laser output power density at the surfaceof cover 16 and the rate at which cover 16 moves relative the beam 14.

In another process, laser source 12 may be controlled to generate pulsesof a laser output beam, each pulse removing by heat ablation orcombustion a minute quantity of cover 16 material. Depth is thereforecontrolled by applying a particular number of pulses before moving to anadjacent, possibly overlapping, site on the inside of cover 16. Thepulsed laser technique combined with a stepwise movement of cover 16should result in superior control over the process when a computer basedcontroller 26 is used.

Multiaxis positioning system 17 may be driven by a multiplicity ofelectric motors controlled by a small computerized controller 26 asshown, or alternatively, by electromechnical actuation of a multiplicityof cams and mechanical devices which move the cover 16 in a properpattern at appropriately controlled rates.

In most industrial applications, the focusing elements 18 must bemaintained clean and free of blowback debris emanating from the scoreline 20. A free flowing gas system 28 is frequently employed to achievefocusing element 18 cleanliness. Also, certain gases, if directed to thescore line 20 formed at the laser impingement area, will alter thechemistry and thermodynamics at the scoring site. For example, inertgases such as nitrogen or argon can displace the oxygen in the air atthe impingement site and prevent both charring and local combustionwhile keeping the focusing elements clean. Alternate gases and flowrates can dramatically alter the properties of the resulting score line20 and create a wide range of physical properties of the cover 16.

FIG. 3 shows yet another embodiment in which the cover 16 is maintainedin a fixed position and the laser output beam 14A is manipulated by asystem of controlled positioning translating mirrors 30 and a controlledpositioning focusing system 32.

FIG. 4 illustrates a preferred form of the invention, in which aself-contained laser generator 34 is mounted to a robot arm manipulator36, which moves the laser generator 34 under program control stored in acentral computer control 38 and directing a robot controller 40, so asto cause a focused laser beam 14B to trace a pattern on a trim piececover 42 corresponding to a programmed score line.

The computer controller 38 may also be connected to a laser controller44 which can vary the operation and power level of the laser generator34.

The cover 42 is fixtured on an ultrasonic sensor 46 which generatessignals corresponding to the thickness of material remaining after thegroove scoring is produced by the laser beam 14B such as to provide afeedback signal to the central computer control 38 to vary the positionof the laser generator 34 and/or its power output to precisely controlthe thickness of material remaining after the groove scoring isproduced. The resistance to tearing of the remaining material above thegroove is important to proper air bag deployment and hence its thicknessshould be controlled.

Such ultrasonic sensors capable of gauging internal features, such asmaterial thickness, are commercially available, and hence details arenot here given.

The laser generator 34 is preferably of the “diffusion cooled” typewhich does not require gas line hookups and thus is readily mountable toa robot arm manipulator. Accordingly, the optical system is simplifiedas the beam is directed by robot arm motion, lower costs and improvingperformance. A more rugged, reliable installation also results, suitedto a production environment.

Diamond™ lasers available from Convergent Energy of Sturbridge, Mass.are perfectly suited for this application.

FIG. 4A shows a variation wherein a second robot arm 36A is providedwhich manipulates a gauging laser beam generator 48, directing andreflects low power laser beam 52 upon the cover 42, which reflectedlaser beam is detected and analyzed in a laser gauging circuit 50. Fromthis, there is developed a signal in the laser gauging circuit 50indicating the precise location of the cover surface at a point justahead of the cutting laser 14B. This allows the central computer control38 to cause the position of the cutting laser beam generator 34 to beshifted by the robot arm 36 correspondingly (or to adjust the outputbeam) so as to maintain a groove depth which will produce a constantthickness of remaining material.

The laser beam can be directed to not only produce the scoring of thecover 42, but may produce cutout openings 54 therein. Further, theperimeter of a substrate panel 56 to which the cover 42 is assembled canbe trimmed as well, achieving significant manufacturing economies.

FIGS. 5 and 5A illustrate the application of the above-described processto a cover panel 58 formed by a dry powder slush molding operation. Thisprocess is commercially practiced by depositing a powder on a heatedmold surface, which results in a smooth outer surface 60, grained andpainted, which is exposed within the passenger compartment. The othersurface 62 is relatively rough, and hence a relatively varying depthgroove 64 is necessary to leave a constant thickness t of a remainingmaterial. The thickness t must be controlled to achieve a predictabletearing strength and to avoid any visible indication on the outersurface 60.

Thus, gauging of the thickness t, as with an ultrasonic gage, isnecessary, varying the depth of the groove 64 to maintain the thicknesst.

FIG. 6 shows a segment of a cover 66 vacuum formed from smoothcalendared sheet vinyl. In this case, the groove 68 may be of constantdepth inasmuch as both surfaces are smooth and the combined thickness t₁of the remaining material is constant.

In both examples, the covers 58, 66 are assembled in a mold afterscoring, together with an instrument panel substrate (not shown), andfoam injected into an intervening space to bond together the substrateand cover, as well as deployment door panels and frame, into a unitarytrim piece.

FIGS. 7 and 8 illustrate the process applied to an injection moldedwheel cover 70, having an air bag receptacle indicated in phantom at 72,aligned with a preweakening pattern 74 arranged beneath the main outersurface 76, which may be grained and painted, as indicated.

The preweakening pattern consists of a series of laser scored grooves 78in the inner or rear face 80.

The width w of the groove is sufficient to avoid self healing. Thethickness t_(L) of the material remaining above the laser beam scoredgroove 78 may be less than the remaining thickness t_(M) of a moldedgroove and still remain invisible from the finished surface 76.

it is also noted that the laser scoring process can be carried out veryrapidly, and saves processing time over the molding time where a longcooling interval is required to avoid cracking over the thinned outregion above the preweakening groove.

The scoring depth can vary from 20%-80% of the total thickness dependingon the available tearing force, the strength of the material used, andwhether or not other assisting devices are employed.

FIGS. 9 and 10 show the application of the process of vinyl claddingcovers. In FIG. 9, an outer vinyl layer 102 is bonded to a polypropylenefoam backing layer 106 to form a composite cover. Laser scored grooves104 extend into the rear face to various exemplary depths, i.e.,partially into layer 106, completely through the layer 106, or partiallythrough the covering layer 102. The groove depth required depends on theneeds of the particular application, i.e., the level of force designedto cause rupture of the preweakened seam.

In FIG. 10, the vinyl cladding layer 102 and backing layer 106 arevacuum formed and adhesively bonded to a thermoplastic substrate 108. Inthis case, the laser scored grooves 110 also penetrate the substrate108.

FIGS. 11 and 12 illustrate the process applied to a leather cover 82. InFIG. 11, a groove 84 is laser scored into a zone 86 which has beenpretreated with lacquer to be more notch sensitive as described indetail in copending U.S. Ser. No. 08/109,122, filed Aug. 13, 1993.

In FIG. 12, a groove 90 is laser scored into an untreated leather cover88.

FIG. 13 illustrates the process applied to a cosmetic cover layer 92,shown as a textile material as might be used with a side impact air bagsystem, which has a scrim backing layer 94 bonded thereto.

The laser scored groove 95 penetrates completely through the backingscrim 94 and partially through the textile layer 92.

FIGS. 14 and 15 show applications to miscellaneous composites.

In FIG. 14, a cosmetic skin 96, such as a vacuum formed vinyl sheet, isapplied over a metal substrate 98 (such as aluminum or steel). In thisinstance, the laser scoring forms a groove 100 completely penetratingthe metal substrate 98 and partially penetrating the cover skin layer 96to create the preweakening.

FIG. 15 shows a skin 96A over scrim backing 98A, penetrated with thelaser scored groove 100A.

Referring to FIG. 16, a laser generator 112 can direct a laser beam 114at the reverse side of a substrate panel 116 underlying a cover layer118 and intervening foam layer 120 provided in a skin and foamconstruction.

The power of the laser beam 114 can be controllably varied so as tocompletely penetrate the substrate panel 116 and foam layer 120, butonly partially penetrate the inside of the cover 118, as indicated,creating the preweakening by a laser scoring.

A deployment door panel 122 is thus formed at the same time, perfectlyaligned with the preweakening pattern of the cover 118.

The use of a laser beam enables preweakening by other forms than astraight groove.

As shown in FIG. 17, a series of round perforations 124 or slots 126 areformed in the cover 128 by intermittent operation of the lasergenerator.

FIG. 18 shows a stepped, variable depth groove 130 formed in a cover 132which varies in depth along its length. This shape may be produced bypulsating operation of the laser generator, resulting in a cyclicallyvarying intensity laser beam.

FIG. 19 shows a localized preweakening of a cover 134 having laserscored preweakening groove 136 formed therein. A series of crossinggrooves 139 are formed across the groove 136 at a selected locale. Thiscreates a preferential intermediate point at which severing will proceedin opposite directions as indicated.

The preweakening process is readily applicable to all conventional typesof trim piece construction, i.e., skin and foam with both vinyl andleather skins (vacuum formed, dry powder, molded, injection molded)vinyl clad, or hard plastic with a surface finish.

1. A process for constructing a preweakened automotive interior trimpiece comprising an instrument panel covering an air bag installation,said preweakening extending in a predetermined pattern enablingformation of an air bag deployment opening in said instrument panel bypressure exerted by an air bag deploying from said air bag installationmounted on the inside of said trim piece, said process including thesteps of: constructing said instrument panel with a thin pliant plasticouter cover layer defining an outer surface extending smoothly anduninterruptedly over said predetermined pattern; preweakening saidconstructed instrument panel by directing a laser beam at an innersurface of said instrument panel and along said predetermined pattern soas to produce a scoring therein partially penetrating an inner surfaceof said outer cover layer along said predetermined pattern; and saidpreweakening step including controlling said scoring by said laser beamso as to cut a series of repeating spaced apart deep scoringpenetrations extending partially into the inside of said trim piececover with intervening uncut material between said deep scoringpenetrations thereby forming a varying depth laser scored groove in saidouter cover layer which has a lower resistance to tearing along saidpredetermined pattern by the pressure exerted by said deploying air bagbecause of the presence of said deep scoring penetrations while saidintervening uncut material strengthens said outer cover layer to reduceany tendency for preweakening said pattern to become visible from saidouter surface prior to air bag deployment or to develop cracks in saidouter cover sensing the remaining thickness of said instrument panelouter cover layer beyond said scoring during said laser beam scoring,and controlling said laser beam scoring in correspondence to said sensedremaining thickness so as to maintain a predetermined minimum remainingthickness of said instrument panel outer cover layer beyond said scoringto avoid cracking along said pattern.
 2. The process according to claim1 wherein said sensing step is carried out using a sensor located on theouter surface side of said instrument panel.
 3. A process forconstructing a preweakened automotive interior trim piece comprising aninstrument panel covering an air bag installation, said preweakeningextending in a predetermined pattern enabling formation of an air bagdeployment opening in said instrument panel by pressure exerted by anair bag deploying from said air bag installation mounted on the insideof said trim piece, said process including: constructing said instrumentpanel with a thin pliant plastic outer cover layer defining an outersurface extending smoothly and uninterruptedly over said predeterminedpattern; preweakening said constructed instrument panel by directing alaser beam at an inner surface of said instrument panel and along saidpredetermined pattern so as to produce a scoring therein partiallypenetrating an inner surface of said outer cover layer along saidpredetermined pattern; said laser beam is controlled during said scoringof said inner surface of said outer cover layer so as to score a seriesof closely spaced repeating partial penetrations into said inner surfaceof said outer cover layer while leaving unscored intervening cover layermaterial between said partial penetrations, said series of repeatingpartial penetrations extending along a path defining said predeterminedpattern and comprising a stepped depth scoring into said inner surfaceof said outer cover layer; and sensing the remaining thickness of saidinstrument panel outer cover layer beyond said scoring during said laserbeam scoring, and controlling said laser beam scoring in correspondenceto said sensed remaining thickness so as to substantially maintain apredetermined minimum remaining thickness of said instrument panel outercover layer beyond said scoring such that said minimum remainingthickness of said instrument panel outer cover layer along saidpredetermined pattern is sufficiently thin to be readily severed by saidpressure exerted by said deploying air bag but sufficiently thick sothat said predetermined pattern will not be visible from said outersurface prior to air bag deployment nor develop cracks in said outercover layer.